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E.A. Nauman, E.A. Sander, J.C. Downs, R.T. Hart, C.F. Burgoyne; Comparison of Animal Eye Geometries and Their Impact on Ocular Biomechanics . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1270.
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Purpose: To compare the geometry dependent stresses developed in the sclera and scleral canal of different animal species. Methods: Morphological data reported in the literature for human, monkey, pig, and rabbit studies were used to generate archetypal geometries for each species. Stress in the sclera was estimated from the law of Laplace. Stress concentrations arising in the peripapillary sclera were estimated using relationships for uniaxial and biaxial loading of a hole in an infinite plane and for a hole in a pressurized spherical shell. A sensitivity analysis was conducted to determine the importance of each geometric parameter. Results: Scleral stress in the pig was 5 x IOP and 21 x IOP in the rabbit. Scleral stress in human and monkey eyes were 6 and 17 x IOP, respectively. The stress in the peripapillary sclera calculated with the uniaxial stress amplification equations were between 3 and 5 times the scleral stress, while the biaxial stress amplification equations ranged between 2 and 4 times the scleral stress, regardless of the animal specific geometry. The maximum peripapillary stress calculated from the equation for a hole in a pressurized spherical shell varied over a wide range spanning between 16 x IOP and 186 x IOP. A change in axial length contributed to the variation in the amplification between species but to a lesser extent than a change in scleral thickness. A sensitivity analysis in which the axial length and scleral thickness were independently varied by 10% changed the stress amplification 2% to 3%. Changing the scleral canal diameter by 10% amplified the stress 5%. Conclusions: Significant differences in the scleral stress were found between animals. Furthermore, the stress amplification around the scleral canal demonstrated a surprisingly wide range of stresses between species, which were a direct result of scleral shell and canal geometry.
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